Performance improvement of euv photoresist by ion implantation

ABSTRACT

A method of patterning a substrate may include providing a blanket photoresist layer on the substrate; performing an ion implantation procedure of an implant species into the blanket photoresist layer, the implant species comprising an enhanced absorption efficiency at a wavelength in the extreme ultraviolet (EUV) range; and subsequent to the performing the ion implantation procedure, performing a patterned exposure to expose the blanket photoresist layer to EUV radiation.

RELATED APPLICATIONS

This application is a divisional of, and claims the benefit of priorityto, U.S. Patent Application Ser. No. 15/786,806, filed Oct. 18, 2017,entitled “Performance Improvement Of EUV Photoresist By IonImplantation,” which is a non-provisional of U.S. Provisional PatentApplication 62/547,418, filed Aug. 18, 2017 entitled “PerformanceImprovement Of EUV Photoresist By Ion Implantation,” the entirety ofwhich applications are incorporated herein by reference.

FIELD OF THE DISCLOSURE

The disclosure relates generally to techniques for manufacturingdevices, and more particularly, to techniques for improving photoresistfor patterning substrates.

BACKGROUND OF THE DISCLOSURE

Known photoresist materials, including chemically amplified photoresists(CAR) face many challenges for application in Extreme Ultraviolet (EUV)lithography. To achieve higher resolution and/or lower line-edge andline-width roughness (LER/LWR), the CAR materials demands entail a highEUV dose, which high dose may be uneconomical given the high cost of EUVpower. For example, up to 96% of EUV power is lost in optics of an EUVsystem before EUV radiation reaches a substrate to be exposed. In thelast few years, alternative photoresist systems such as metal-oxidephotoresist and metal-containing photoresist have been explored.Advantages provided by such alternative photoresist systems includeincreased absorption of incident EUV photons as well as better etchselectivity, allowing thinner photoresist layers to be used forpatterning of a substrate.

There are also several limitations for the use of known metal-oxide ormetal-based photoresist architecture. One limitation is the finitelifetime of photoresist materials that incorporate metal-oxidenanoparticles into a photoresist matrix. In order to provide acceptableshelf life these photoresist materials may employ a stabilizer tostabilize a nanoparticle suspension, adding to cost and reducingsensitivity of the photoresist material.

Moreover, dispensing and maintaining an acceptable degree of uniformityof nanoparticle suspension within a photoresist at the nanometer lengthscale may be particularly challenging. Many of the sensitizers that maybe used in a photoresist formulation also readily sublime during a softbake operation, resulting in additional non-uniformity. Thisinhomogeneity may lead to difficulty in controlling LWR, as well asdifficulty in controlling critical dimension (CD).

Because metal-based photoresists are highly etch-resistant, metal-basedphotoresists may be applied as thinner layers for patterning a substratethan conventional CAR materials, as thin as ˜15 nm, for example. Thethinner film imparts the advantage of being less susceptible to patterncollapsing, but also entails a smaller photoresist volume and thus lessphotons being absorbed. Accordingly, more noise and worse LER/LWR mayresult from such thin photoresists. Increasing the film thickness, runsthe risk of generating a patterned photoresist feature having a“T-topping” structure, where the photoresist feature may exhibit a “T”shape in cross-section after patterning and development. That is, thephoton availability attenuates as a function of thickness of thephotoresist, due to strong absorption by the metal sensitizers. Becauseof greater photon density at the top of a photoresist feature, and sincemost existing metal-based photoresists are negative tones, this photonattenuation results in a photoresist profile resembling a “T” or areversed pyramid. While negative tone photoresists in general are betterfor improving small pitch resolution this advantage is offset by theT-topping problem.

Another issue with the employment of photoresist containing metal oxideparticles or metal particles is that metal hydrides may form in ascanner of a EUV lithographic tool due to reaction between thephotoresist and hydrogen used in the scanner. The metal hydrides maydeposit on the EUV mirror surfaces, reducing optics lifetime.

With respect to these and other considerations, the present embodimentsare provided.

BRIEF SUMMARY

In one embodiment, a method of patterning a substrate may includeproviding a blanket photoresist layer on the substrate; performing anion implantation procedure of an implant species into the blanketphotoresist layer, the implant species comprising an enhanced absorptionefficiency at a wavelength in the extreme ultraviolet (EUV) range. Themethod may further include, subsequent to the performing the ionimplantation procedure, performing a patterned exposure to expose theblanket photoresist layer to EUV radiation.

In another embodiment, a method of enhancing a photoresist layer mayinclude: applying the photoresist layer as a blanket photoresist layeron a substrate; and prior to patterning the blanket photoresist layer,performing an ion implantation procedure of an implant species into theblanket photoresist layer, the implant species comprising an enhancedabsorption efficiency at a wavelength in the extreme ultraviolet (EUV)range, the enhanced absorption efficiency being greater than 2×10⁶cm²/mol.

In an additional embodiment, a method of improved patterning of aphotoresist layer, may include providing an underlayer on a substrate.The method may include performing an ion implantation procedure of animplant species into the underlayer, the implant species comprising anenhanced absorption efficiency at a wavelength in the extremeultraviolet (EUV) range, the enhanced absorption efficiency beinggreater than 2×10⁶ cm²/mol. The method may also include applying thephotoresist layer as a blanket photoresist layer on the underlay; andpatterning the blanket photoresist layer by exposure to EUV radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary process flow according to embodiments of thedisclosure.

FIG. 2 shows a graph depicting general trends in EUV absorption as afunction of atomic number.

FIG. 3 presents a graph depicting simulation results of sputtering yieldand Rp for 0.5 keV Sn implantation as a function of different ionincident angles.

FIG. 4 illustrates photon profile of EUV photons and implant profiles ofimplant species as a function of depth in a photoresist layer, accordingto embodiments of the disclosure.

FIG. 5 illustrates a photoresist structure after patterning by EUVexposure.

FIGS. 6A-6C illustrate operations involved in a process, according toother embodiments of the disclosure.

The drawings are not necessarily to scale. The drawings are merelyrepresentations, not intended to portray specific parameters of thedisclosure. The drawings are intended to depict typical embodiments ofthe disclosure, and therefore are not to be considered as limiting inscope. In the drawings, like numbering represents like elements.

DETAILED DESCRIPTION

A material and method in accordance with the present disclosure will nowbe described more fully hereinafter with reference to the accompanyingdrawings, where embodiments are shown. The method and materials may beembodied in many different forms and are not to be construed as beinglimited to the embodiments set forth herein. Instead, these embodimentsare provided so this disclosure will be thorough and complete, and willfully convey the scope of the system and method to those skilled in theart.

As used herein, an element or operation recited in the singular andproceeded with the word “a” or “an” is to be understood as includingplural elements or operations, until such exclusion is explicitlyrecited. Furthermore, references to “one embodiment” of the presentdisclosure are not intended as limiting. Additional embodiments may alsoincorporating the recited features.

In various embodiments, methods and material are provided for enhancinglithography, such as for enhancing extreme ultraviolet lithography. Insome embodiments, an improved photoresist is provided by performing anion implantation procedure to enhance EUV sensitivity of the photoresistbefore patterning in an EUV scanner is performed.

In particular, the ion implantation procedure may introduce an implantspecies that enhances EUV sensitivity of the photoresist at thepoint-of-use (POU) of the photoresist, such as when the photoresist isprovided as a blanket photoresist layer on a substrate to be exposed.

FIG. 1 depicts a process flow 100 according to embodiments of thepresent disclosure. At block 102, a blanket photoresist application isperformed to form a blanket photoresist layer on a substrate. Theblanket photoresist may be an EUV photoresist having a knowncomposition. While not limited to a particular thickness, in someembodiments the blanket EUV photoresist layer may have a thicknessbetween 10 nm and 100 nm, between 15 nm and 100 nm, and in particularembodiments less than 50 nm or less than 30 nm. Thinner EUV photoresistlayers may be especially appropriate to print features within the EUVphotoresist layer having critical dimensions of less than 50 nm, lessthan 25 nm, and in some examples, less than 15 nm. Notably, the blanketEUV photoresist layer may have a uniform composition and may not includeadditives such as metal oxide particles or metal particles, where theproblems resulting from the use of such particle additives have beendetailed above.

At block 104, a soft bake of the blanket photoresist layer is performed.The soft bake may be performed according to known techniques forprocessing photoresist layers, in particular, EUV photoresist layers,before EUV exposure.

At block 106, a point-of-use ion implantation procedure is performed,meaning the implantation procedure is performed shortly before thesubstrate is exposed to an EUV exposure to pattern the blanket EUVphotoresist layer. An implant species that enhances EUV sensitivity isimplanted into the blanket EUV photoresist layer in the point-of-use ionimplantation procedure. As detailed below, the implant species may beone of a number of different species, where the ion energy (implantenergy) and ion dose is tailored according to the layer thickness ortailored to other features of the blanket EUV photoresist layer, inorder to enhance the EUV lithographic exposure process to follow. Inparticular, the implant species may exhibit a high absorption efficiencyat a wavelength in the extreme ultraviolet (EUV) range, such as at ornear 13.5 nm.

At block 108, lithographic exposure of the blanket photoresist layerincluding the implant species is performed using EUV radiation. Theexposure may perform patterning according to known EUV lithographictechniques. By virtue of the enhanced EUV sensitivity provided by theimplant species, the duration of the EUV exposure to achieve a targetlithographic result may be reduced in comparison to the use ofconventional EUV photoresist materials.

At block 110 a post exposure bake may be performed according to knownprocesses, while at block 112 photoresist development may be performedto produce the desired features, such as nanometer-scale photoresistfeatures.

In particular embodiments, the implant species used in the point-of-useimplantation operation described above may exhibit multiple usefulproperties. For one, the implant species may enhance the absorption ofEUV radiation in the blanket photoresist material. For another, theimplant species may constitute a material that is suitable for use in anion source, plasma, or other source of implanting ions. For another, theimplant species may be relatively safe or non-toxic.

In particular embodiments, tin (Sn) may be employed as an implantspecies for enhancing EUV absorption. An advantage provided by Sn is thevery large absorption cross-section for EUV radiation as compared to themain constituent elements of known EUV photoresist materials. Turningnow to FIG. 2, there is shown a graph depicting general trends in EUVabsorption as a function of atomic number (Z). As illustrated, theregion 200 includes elements that are the main constituents of EUVphotoresist, including carbon, oxygen, nitrogen, and hydrogen. In thisregion of the periodic table, the EUV absorption is less thanapproximately 2×10⁶ cm²/mol. In contrast, as shown in FIG. 2, theabsorption of Sn is approximately 1.4×10⁷ cm²/mol. This largeenhancement in EUV absorption shown by implant species Sn accordinglymay impart a much larger EUV sensitivity to a blanket EUV photoresistlayer after implantation with the appropriate dose in the range of 5e14to 1e17 ions/cm², depending on a number of factors such as the resistformula, resist density, initial resist thickness, targeted sensitivityimprovement, tendency to form T-topping, and so forth.

In various embodiments, the ion energy for implanting Sn may range froma few hundred eV to a few kV, where the exact energy may be tailored tothe thickness of the blanket EUV photoresist layer being implanted. Asnoted previously, in some examples this thickness of the blanket EUVphotoresist layer may be in the range of 10 nm to 50 nm. By choosing theappropriate ion energy and ion dose for implanting Sn ions, a largeenhancement in EUV sensitivity may be imparted into an EUV photoresistlayer, while not unduly damaging the materials of the EUV photoresistlayer.

Table 1, shown below, lists the energy, projected range, and sputteringyield, generated by TRIM simulations using Sn as an example implantingspecies, and using a surrogate substrate that contains Sn, C, O, and H.Under these conditions, the sputtering yields are sufficiently low thatreduction in layer thickness of an EUV photoresist layer due toresputtering by implanting Sn ions is not a major consideration. Thetotal ion penetration depth (implant depth), roughly twice of the Rp orprojected range, is approximately 20 nm, comparable to the thickness ofpresent-day metal oxide photoresists, such as photoresists containingtin oxide, hafnium oxide, or other oxide material. In variousembodiments, this blanket photoresist to be implanted may be made of aplain conventional CAR, or a metal oxide photoresist without the metalcomponents, or a regular metal oxide photoresist. In this manner, thephotoresist after implantation may exhibit improved photosensitivitywith respect to conventional photoresists, or may show further improvedphotosensitivity with respect to metal oxide photoresists, and may alsoshow decreased or eliminated T-topping through non-uniform sensitizerprofile.

TABLE I Energy of Sn (keV) Projected Range (nm) Total Sputtering Yield0.5 8.5 0.120 1.0 10.7 0.311

FIG. 3 presents a graph depicting simulation results of sputtering yieldand Rp for 0.5 keV Sn implantation as a function of different ionincident angles, with respect to normal incidence. The sputtering yieldand Rp do not change significantly in this example at incident anglesbelow 30°. This insensitivity toward ion incident angle at low angleshas several implications. For one, the insensitivity in properties atlow incidence angle means that Sn implantation may be readily performedin a variety of different apparatus. For example, beamline implantersmay be used for Sn implantation, where incidence angle may readily beadjusted, including normal incidence. For another, plasma immersionsystems may be used where incidence angle of ions extracted from aplasma may be approximately normal to a substrate being implanted. Insystems that employ plasma chambers having extraction apertures todirect an ion beam to a substrate in an adjacent chamber, at least someions may emerge from the plasma chamber having trajectories that form alow incidence angle with respect to normal, such as below 30 degrees.Accordingly, these “extraction aperture” systems may additionally beappropriate for Sn implantation.

An additional implication of the results of FIG. 3 is that the incidenceangle may be tuned at intermediate angles to adjust the implantationrange. For example, at 45 degrees incidence, the value of Rp is reducedby approximately 30% with respect to normal incidence to a value of 6nm. This reduction of Rp may be useful to accommodate Sn within thinnerphotoresist layers, while not penetrating into an underlying substrate,bearing in mind the total implantation range may be approximately twiceRp. For example, according to FIG. 3, at 500 eV the total range in EUVphotoresist of implanting Sn at normal incidence may be estimated to be16 nm, while at 45 degrees the total range may be estimated to be 12 nm.Accordingly, a 12 nm thick EUV photoresist layer may be implanted with500 eV Sn ions at 45 degrees while not penetrating to an underlyingsubstrate, while a 12 nm thick EUV photoresist layer implanted at normalincidence may fail to stop a certain fraction of ions from penetratinginto the underlying substrate. While Rp may also be reduced by reducingion energy, in some cases practical considerations such as the amount ofion current extractable from an ion source or plasma source for lowenergies, or the ability to properly direct a low energy ion beam to asubstrate, may preclude use of lower energies.

Notably, while the sputter yield at 45 degrees may be larger than atzero degrees (normal incidence), the sputter yield may still beacceptably low so as to employ such an angle for Sn implantation.

In various additional embodiments, an implant species may be a gaseousspecies at room temperatures. In one embodiment, Xe may be employed asan implant species for implanting into a blanket EUV photoresist layer.Other suitable implant species include In, Sb, and I. The embodimentsare not limited in this context. Any element(s) showing enhancedabsorption efficiency at a wavelength in the EUV range (approximately13.5 nm) may be suitable for implant species, where “enhanced absorptionefficiency” may indicate an EUV absorption cross-section that is greaterthan the EUV absorption cross-sections for H, C, N, or O, meaninggreater than 1.5×10⁶ cm²/mol. Examples of other suitable elementsinclude I, Te, In, and Sb. Notably, at least some elements having atomicnumbers in the range of 25-25 and 65-75 may also be suitable for use asEUV enhancers. The embodiments are not limited in this context.

Returning now to FIG. 2, the graph also indicates Xe, showing a highabsorption cross section of approximately 1.6×10⁷ cm²/mol. As a noblegas element, Xe may readily be employed in a beamline ion implanter,plasma immersion apparatus, or compact plasma source apparatus having anextraction aperture, among other tools. Because Xe is a noble gas, Xecannot be readily incorporated in photoresist layers by methods such asparticle dispersion, blending, or other liquid or solid-state methods.In the present embodiments, Xe may be readily dispersed into photoresistby implantation as monatomic ions. In this manner, the element providingenhanced EUV absorption (Xe) may be uniformly dispersed into aphotoresist at least to the nanometer level, a result not achievable bydispersion of metal oxide or metal particles according to knowntechniques. The same applies to implantation of Sn, discussed above.

In various additional embodiments, implantation into blanket EUVphotoresist may be performed to tailor the implant profile to accountfor the nature of EUV exposure. FIG. 4 illustrates a photon profile 220of EUV photons as a function of depth in a photoresist layer. Asevident, the intensity of photons decreases in a generally exponentialmanner with increasing depth from the outer surface. This decrease inintensity means that portions of a photoresist layer located at greaterdepths from the surface of a photoresist layer may receive less photonexposure. In the case of a negative tone photoresist, this phenomenonmay result in the generation of a patterned resist structure 230 afterexposure to an EUV patterning operation, as shown in FIG. 5. Thepatterned resist structure 230 is shown in profile, where portions ofthe patterned resist structure 230 closer to the substrate 234 aredeeper from the surface of the original blanket photoresist layer.Accordingly, portions of the original photoresist layer closer to thesurface receive more photo exposure, resulting in the overhang portions232, as shown.

In accordance with various embodiments, an ion implantation recipe orprocess is adjusted to compensate for the photon decay as exhibited inFIG. 4, by placing a higher concentration of implant species atlocations removed from the photoresist surface. As an example, implantprofile 222 represents an implant profile for Sn species, Xe species, orother species exhibiting an enhanced EUV absorption in comparison thephotoresist matrix that hosts the implant species. As shown, the implantprofile 222 exhibits a peak at approximately 12 nm below the photoresistsurface. In this manner, the relative amount of absorption of EUVphotons that reach a depth of 12 nm is enhanced, at least partiallycompensating for the general reduction in photons as exhibited by thephoton profile 220.

In particular embodiments, multiple ion implants of an implant species,such as Sn or Xe may be performed into the blanket photoresist layer.The multiple implants may be used to generate a composite implantprofile that is a non-uniform depth profile, functioning to moreeffectively compensate for the photon decay as a function of depth in aphotoresist layer. FIG. 4 exhibits a shallow implant, shown as implantprofile 224 and a deep implant, shown as implant profile 226. Togetherwith the implant profile 222, these implant profiles may act to generatea more uniform photon absorption profile as a function of depth in aphotoresist layer, such as a 25 nm thick photoresist layer in theexample of FIG. 4. As a consequence, a more uniform profile of apatterned resist structure may be formed after exposure to EUVradiation, as exhibited by the rectangular portion of the patternedresist structure 230.

In further embodiments of the disclosure, rather than incorporating aspecies having enhanced EUV absorption efficiency by directly implantinginto a photoresist layer, the species may be implanted into anunderlayer, before a photoresist layer is deposited thereon. FIG. 6A,FIG. 6B, and FIG. 6C depict a scenario where implantation of a speciesfor enhanced EUV absorption efficiency, implant species 254, is directedto an underlayer 250, before deposition of a photoresist layer 252. Inparticular, the ion energy of implant species 254 may be tuned toimplant into a top region near a top surface of the underlayer 250,where the underlayer 250 may represent a known underlayer material usedin EUV processes. Exemplary ion energies may range from a few hundred eVto 2000 eV. The top region near a top surface of underlayer 250 mayaccordingly represent a depth of approximately 25 nm or less, or 15 nmor less in some embodiments. Photoresist layer 252 may be applied as inknown techniques (FIG. 6B). When subject to EUV radiation, the additionof the implant species 254 along an interface between the underlayer 250and photoresist layer 252 generates additional photoelectrons 258 (FIG.6C) to help offset EUV photon decay that occurs as a function ofincreasing depth from the top surface of the photoresist layer 252, asdiscussed above. This arrangement also helps minimize T-topping, theappearance of footing on a photoresist feature, and well as minimizingline edge roughness and linewidth roughness.

An advantage afforded by the present embodiments is the ability togenerate a photoresist layer with enhanced EUV sensitivity, just at thepoint of use, in other words, just before a lithography patterningoperation is to be performed, such as within 5 hours, within severalhours, or even within several minutes. This point-of-use capabilityavoids problems with non-uniformity, or aging that may occur in knownmetal oxide resists, where metal oxide particles may settle,agglomerate, redistribute, or otherwise react with resist, when storedin bulk fashion, such as a container. Another advantage is the abilityto uniformly disperse an EUV-sensitive species, such as Sn or Xe at theatomic level within a photoresist layer, since the species may beimplanted as monatomic ions. This advantage may be especially useful forapplications where the total thickness of a photoresist layer is 20 nmor less.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are in the tended to fall within the scopeof the present disclosure. Furthermore, while the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize the usefulness of the present embodiments isnot limited thereto and the present embodiments may be beneficiallyimplemented in any number of environments for any number of purposes.Thus, the claims set forth below are to be construed in view of the fullbreadth of the present disclosure as described herein.

1. A method of improved patterning of a photoresist layer, comprising:providing an underlayer on a substrate; performing an ion implantationprocedure of an implant species into the underlayer, the implant speciescomprising an enhanced absorption efficiency at a wavelength in anextreme ultraviolet (EUV) range, the enhanced absorption efficiencybeing greater than 2×10⁶ cm²/mol; applying the photoresist layer as ablanket photoresist layer on the underlayer; and patterning the blanketphotoresist layer by exposure to EUV radiation.
 2. The method of claim1, wherein the implant species is implanted into a top region near a topsurface of the underlayer.
 3. The method of claim 1, wherein the implantspecies is Xe.
 4. The method of claim 1, wherein the implant species isSn.
 5. The method of claim 1, wherein performing the ion implantationprocedure comprises generating a peak in a concentration of the implantspecies as a function of depth below an outer surface of the underlayer.6. The method of claim 1, wherein the implant species comprises agaseous species at room temperature.
 7. The method of claim 1, wherein aconcentration of the implant species as a function of depth below anouter surface of the underlayer increases to a depth of at least 5 nm.8. The method of claim 1, wherein the ion implantation procedurecomprises a plurality of ion implantation procedures, wherein an implantdepth varies between the plurality of implant procedures.
 9. The methodof claim 8, wherein the plurality of implantation procedures generates anon-uniform depth profile of the implant species as a function of depthin the underlayer, wherein a concentration of the implant speciesincreases as a function of depth within the underlayer.
 10. The methodof claim 1, wherein an ion energy of the implant species is in a rangeof 300 hundred eV to 2000 eV.
 11. The method of claim 1, wherein thewavelength in the EUV range is 13.5 nm.
 12. The method of claim 1,wherein a thickness of the blanket photoresist layer is between 15 nmand 100 nm.
 13. The method of claim 1, wherein the blanket photoresistlayer comprises a metal oxide photoresist, containing metal oxideparticles.
 14. The method of claim 1, wherein an ion energy of theimplant species is less than 1000 eV, and wherein an incidence angle ofthe implant species is greater than 30 degrees with respect to a normalto a plane of the substrate.